The present application relates to magnetic resonance imaging (MRI) apparatuses and systems, and to methods for using such apparatuses and systems.
In magnetic resonance imaging, an object to be imaged as, for example, a body of a human subject is exposed to a strong, substantially constant static magnetic field. The static magnetic field causes the spin vectors of certain atomic nuclei within the body to randomly rotate or “precess” around an axis parallel to the direction of the static magnetic field. Radio frequency excitation energy is applied to the body, and this energy causes the nuclei to precess in phase and in an excited state. As the precessing atomic nuclei relax, weak radio frequency signals are emitted; such radio frequency signals are referred to herein as magnetic resonance signals.
Different tissues produce different signal characteristics. Furthermore, relaxation times from the excited state (also referred to as a T1 relaxation time), as well as from in-phase precession (also referred to as a T2 relaxation time) are the dominant factors in determining signal characteristics. In addition, tissues having a high density of certain nuclei will produce stronger signals than tissues with a low density of such nuclei. Relatively small gradients in the magnetic field are superimposed on the static magnetic field at various times during the process so that magnetic resonance signals from different portions of the patient's body differ in phase, amplitude and/or frequency. If the process is repeated numerous times using different combinations of gradients, the signals from the various repetitions together provide enough information to form a map of signal characteristics versus location within the body. Such a map can be reconstructed by conventional techniques well known in the magnetic resonance imaging art, and can be displayed as a pictorial image of the tissues as known in the art.
The magnetic resonance imaging technique offers numerous advantages over other imaging techniques. MRI does not expose either the patient or medical personnel to X-rays and offers important safety advantages. Also, magnetic resonance imaging can obtain images of soft tissues and other features within the body which are not readily visualized using other imaging techniques. Accordingly, magnetic resonance imaging has been widely adopted in the medical and allied arts.
Despite the wide adoption of magnetic resonance imaging, X-ray detection continues to be the primary method used to image certain features or regions of a patient's anatomy. One such anatomical feature or region is the patient's cranio-cervical junction, which is the area of the body where the skull meets the spine. Imaging the cranio-cervical junction (hereinafter, cranio-cervical junction) is important for several reasons. Firstly, the C1 (atlas) and C2 (axis) vertebrae of the patient are positioned at the cranio-cervical junction, and damage to these vertebrae can pose serious and potentially fatal health risks for a patient. For instance, rotation of either the C1 or C2 vertebra can impact cerebral spinal fluid flow to and from the brain. If one of the C1 or C2 vertebrae is rotated improperly, it can significantly cut off flow of the cerebral spinal fluid, which can in turn create pressure buildup in the patient's brain.
Despite the importance of imaging the cranio-cervical junction, repeated imaging, such as for the purpose of monitoring the cranio-cervical junction, would require repeated exposure to X-rays. This repeated exposure itself cause damage to living tissue. It is, therefore, recommended that efforts to reduce exposure continue and that repeated X-ray exposure should be minimized. MRI exams, by comparison, can be repeatedly performed without health concerns, and can provide the same or better level of image detail as can X-ray imaging. In that regard, it is desirable to develop a method of imaging the cranio-cervical junction using MRI.
One drawback to imaging the cranio-cervical junction using MRI systems and methods currently known in the art is poor image quality. Acquiring a high quality image using MRI generally requires maintaining a good signal-to-noise ratio (SNR) between the magnetic resonance signals and any accompanying noise. Achieving a good SNR, or at least an improved SNR, often requires the imaging coil of the MRI system to be placed as close as possible to the anatomy of interest. In the case of the cranio-cervical junction, the anatomy of interest is positioned between the patient's skull and spine, making it difficult to image the cranio-cervical junction using a standard head coil or cervical coil. As such, there is a need for a new coil that improves the SNR of cranio-cervical junction images.
Furthermore, imaging a particular anatomical feature or anatomy of interest within the cranio-cervical junction requires the MRI system to be properly aligned with the anatomy of interest. As such, there is also a need for a coil that has a field sensitivity that corresponds with an orientation or alignment of the coil within the MRI system (e.g., a field sensitivity perpendicular to the main magnetic field.